1. Field of the Invention
This invention generally relates to a method for manufacturing a circuit board, and more particularly, to a method for manufacturing a circuit board by means of electrophoretic deposition.
2. Description of the Related Art
Accompanying with the development of technologies and improvement of life quality, the requirements of the electronic products by consumers are not only to be powerful but also to be light, compact and lower-energy consuming. Accordingly, the integration of commercial electronic products has become higher and the function thereof has become powerful.
In order to conform to the trend aforementioned, circuit boards of the electronic devices packaged inside electronic products are developed gradually from single layer to multilayers, e.g. two layers, four layers, eight layers or even more than ten layers, such that the electronic devices can be mounted on the circuit boards with higher density so as to miniaturize the electronic products.
Referring to FIGS. 1A to 1C, they schematically illustrate a conventional method for manufacturing a circuit board, and a circuit board with four wiring layers is taken as an example herein. Referring to FIG. 1A, a substrate 10 is provided and a first wiring layer 11 is formed respectively on the front and back sides of the substrate 10, wherein the first wiring layer 11 is formed by means of lithography, developing and etching processes know in the art.
Referring to FIG. 1B, after the first wiring layers 11 are formed on both sides of the substrate 10, an insulating dielectric layer 12 and a copper foil 13 which is attached on the dielectric layer 12 are laminated on the first wiring layer 11 and partially on the substrate 10, wherein the dielectric layer 12 may be a prepreg.
Referring to FIG. 1C, after the dielectric layer 12 and the copper foil 13 are laminated on both sides of the substrate 10, the copper foil 13 is processed with lithography, developing and etching processes so as to form a second wiring layer 14. Then a solder mask layer 15 is formed on the second wiring layer 14 so as to prevent the metal lines from oxidation and arc-welding short-circuit, wherein the solder mask layer 15 is exposed metal lines which are formed through the processes of exposure, developing and partially removing the solder mask layer 15.
Finally, a Pb—Sn layer or a Ni/Au layer is formed on the surfaces of the exposed metal lines so as to protect the lines and be served as contacts 17 for outward connection. In addition, a plurality of through holes 17 can be drilled between the first wiring layer 11 and the second wiring layer 14 for providing electrical connection therebetween.
In the conventional circuit boards, the dielectric layer 12 has a predetermined thickness, generally about 40 micrometers (or from 40 to 100 micrometers). Therefore, if the thickness of the dielectric layer 12 can be reduced, the circuit board can be lighter and more compact. At the same time, more numbers of wiring layers can be manufactured inside a circuit board within a predetermined thickness limitation so as to increase the integration.
Therefore, it is necessary to provide a practical and effective method to solve the insufficient aspects in the art.